1. Field of the Invention
The present invention relates to a communication protocol system used during a communication by a personal computer utilizing an ordinary communication line for public use such as a telephone line.
2. Description of the Prior Art
Currently, users who communicate using a computer with an outside source are remarkably increasing.
Moreover, in proportion to the increase of users who communicate using a personal computer, the quantity of text data such as messages and binary data such as programs to be transmitted and received is also increasing tremendously. For this reason, high efficiency and high reliability transmission are essential for such communication by personal computer.
Transmission control procedures which are generally used for the conventional communication by personal computer include a "non-procedure" used for text data (so-called character data displayed on the screen) and "XMODEM" for binary data not displayed on the screen such as a program execution file.
The "non-procedure" does not substantially provide problems in the transmission efficiency but in reliability.
The latter "XMODEM" does not provide problems in the reliability but in the transmission efficiency due to the transmission format requiring an acknowledgement upon receipt. For instance a packet data is transmitted and received, for example, in sizes unit of 128 bytes, and such a packet data is checked, for example, by a "check sum (csum)" or the receiving side for every packet, and then a check of the transmission by ACK/NAK is carried out, namely "ACK" is returned, when no error is detected but "NAK" is returned when an error is detected. While "XMODE" is a highly reliable method of transmitting data, "XMODE" is not as efficient as the other methods.